Quercetin has strong antioxidant activity and has been shown to support immune health by mediating the release of inflammatory compounds including leukotrienes and prostaglandins. [1,2] Quercetin is known for its ability to stabilize mast cells, diminishing the release of histamine, the compound known to cause hypersensitivity reactions during seasonal changes. 
Stinging Nettles Leaf Extract
Stinging nettles leaf is a plant that has been shown to balance immune response, specifically in the airways and nasal passages.  Studies have shown that the extract of stinging nettles leaf balances a variety of inflammatory activities that affect respiratory health. 
Bromelain is a plant enzyme naturally found on the stem and fruit of the pineapple plant. Bromelain is a proteolytic (protein-digesting) enzyme that aids in in the breakdown of large protein complexes, including antigenic compounds, and has been shown to enhance the absorption of quercetin.  Bromelain has been shown to reduce circulating allergenic protein complexes associated with hyper-immune sensitivity and seasonal discomfort. 
N-acetyl cysteine (NAC) is an amino acid precursor to one of the most important antioxidants in the body, glutathione. Both glutathione and NAC help reduce the viscosity of the mucus allowing for clearing of the airways and improved respiratory health. [9,10]
Vitamin C cannot be synthesized by humans and is therefore an essential nutrient that must be consumed in the diet. Among its numerous health-promoting properties, vitamin C is an essential vitamin that supports the immune system and is also a potent antioxidant. When the body is under a significant amount of stress, vitamin C is excreted rapidly. Vitamin C has many immune boosting properties, but is distinctively beneficial for individuals with seasonal discomfort because of its ability to deactivate histamine.[11,12]
1. Della Loggia R, Ragazzi E, Tubaro A, et al. Anti-inflammatory activity of benzopyrones that are inhibitors of cyco- and lipo-oxygenase. Pharmacol Res Commun 1988;20:91-94. Link to Abstract of Study
2. Kim HP, Mani I, Iversen L, Ziboh VA. Effects of naturally-occurring flavonoids and bioflavonoids on epidermal cyclooxygenase and lipoxygenase from guinea pigs. Prostagladins Leukot Essent Fatty Acids 1998; 58:17-24. Link to Abstract of Study
3. Otsuka H, Inaba M, Fujikura T, Kunitomo M. Histochemical and functional characteristics of metachromatic cells in the nasal epithelium in allergic rhinitis: studies of nasal scrapings and their dispersed cells. J Allergy Clin Immunol 1995 ;96(4):528-36.
4. Mittman P. Randomized, double-blind study of freeze-dried Urtica dioica in the treatment of allergic rhinitis. Planta Med 1990; 56:44-47.
5. Obertreis, B. et al. Anti-inflammatory effect of Urtica dioica folia extract in comparison to caffeic malic acid. Arzneimittelforschung 1996; 46(1): 52-56. Link to Abstract of Study
6. Shoskes DA, Zeitlin SI, Shahed A, Rajfer J. Quercetin in men with category III chronic prostatitis: a preliminary prospective, double-blind, placebo-controlled trial. Urology 1999; 54(6): 960-3. Link to Abstract of Study
7. Cichoke AJ. The Complete Book of Enzyme Therapy. (1999). Garden City Park, NY: Avery Publishing Group.
8. Yim CY, et al. Use of N-acetyl cysteine to increase intracellular glutathione during the induction of antitumor responses by IL-2. J Immul 1994; 152:5796-5805.
9. Ziment, I. Acetyl cysteine: a drug that is much more than a mucokinetic. Biomed Pharmacother 1988; 42(8):513-519.
10. Millar, A.B. et.al. Effect of oral N-Acetyl Cysteine on mucus clearing. Br J Dis Chest 1985; 79: 262-266.
11. Bland JS, Costarella L, Levin B, et al. Clinical Nutrition: A Functional Approach. Second Edition. (2004). Gig Harbor, WA: Institute of Functional Medicine. 12. Johnston CS. The antihistamine action of ascorbic acid. Subcell Biochem 1996;25:189-213.